The overall objective of the proposed research is to define the role of estrogen in the regulation of growth and function in the human uterus. We plan to accomplish this by utilizing the cell culture system recently perfected in our laboratory as an in vitro system for characterizing directly the effects of estrogen on human uterine cells, for comparing the character of response of human endometrial cells to natural and synthetic estrogens and antiestrogens of therapeutic and contraceptive importance, and for analyzing the effects of multiple hormones--progestins, androgens, and thyroid hormones, in particular--on modulation of uterine responsiveness to estrogen. Our studies will take two approaches: (1) Biochemical, assessing hormonal responsiveness in terms of growth stimulation and cell proliferation including indices of enhanced RNA, protein and DNA synthesis in endometrial cells and endometrial tissue cultures, and their relationship to the presence of functional estrogen receptors, and (2) Morphological, determining, in parallel, by phase contrast microscopy, electron microscopy, and scanning electron microscopy the morphological correlates associated with estrogen effects on different human endometrial cells. Studies will include a comparison of the direct effects of hormones on relatively normal endometrium and on pathological endometrium. The unique feature of this in vitro system is that it enables studies to be done directly on human target tissues and therefore eliminates the necessity of extrapolating to human tissue information obtained with experimental animal systems and obviates the difficulties inherent in obtaining information about human reproduction from in vivo studies. Our findings should enable significant progress to be made in understanding how the sex steroid hormones function in human reproduction.